Your old box was single cpu therefore a load of 1 would be one full cycle to complete all the processes in line.

So your .5 load is indeed half your cpu cycle. After you go beyond a load of 1, you will start into your wait time so a load of 1.5 would effectively take 1 1/2 cycles to get through the current tasks.

So with your new box, a load of 2 would indeed require half of your cpu time which is equal to .5 on your old box, that is correct.

A load of 4 would be your full cpu cycle capacity given the threads are evenly stressed, with 0 wait time. You have effectively 4 cpu's multithreaded. You may not notice a lag or wait time until you hit a load of 6 to 8 and still not be a concern.

I have many dual quad boxes with extreme traffic that run happy and cool with a loading of 16 and show no signs of lag or stress. Amazing performance.